1. Field of the Invention
The present invention relates to a valve operating system in an internal combustion engine, including a cam shaft provided with a valve operating cam, a rocker arm having a pair of support wall portions which are integrally connected at their base ends to a swinging support portion swingably supported on a support member mounted on a cylinder head, the support wall portions being opposed to each other at a distance in a direction along the swinging axis of the swinging support portion, a support shaft supported between the support wall portions, and a roller which is rotatably supported on the support shaft with a bearing interposed therebetween, the roller being in rolling contact with the valve operating cam.
2. Description of the Related Art
Such valve operating system is already known from Japanese Patent Application Laid-open No. 63-230916.
The rocker arm in the above known valve operating system is comprised of a swinging support portion swingably supported by a pivot serving as a support member, a pair of support wall portions connected at their base ends to the swinging support portion, and a tip-end connecting portion which connects tip ends of the support wall portions to each other. An engine valve is operatively connected to the tip-end connecting portion, and a roller is rotatably supported on a support shaft supported between the support wall portions to come into rolling contact with the valve operating cam. That face of the swinging support portion, which is opposed to the roller, is formed as a flat surface extending along a plane intersecting a straight line connecting a point at which the swinging support portion is swingably supported by the pivot, to the axis of rotation of the roller. It is difficult to say that the rigidity of the rocker arm of this system is excellent, and desirably the rigidity of the rocker arm should be increased. Moreover, it should be avoided that the size of the rocker arm is increased when its rigidity is increased.
Accordingly, it is an object of the present invention to provide a valve operating system in an internal combustion engine, wherein the rigidity of each of the rocker arms is increased, while avoiding an increase in size of the rocker arm.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a valve operating system in an internal combustion engine, comprising a cam shaft provided with a valve operating cam, a rocker arm having a pair of support wall portions which are integrally connected at base ends thereof to a swinging support portion swingably supported on a support member mounted on a cylinder head, the support wall portions being opposed to each other at a distance in a direction along a swinging axis of the swinging support portion, a support shaft supported between the support wall portions, and a roller which is rotatably supported on the support shaft with a bearing interposed therebetween, the roller being in rolling contact with the valve operating cam, wherein a lower connecting wall interconnecting lower portions of the base ends of the support wall portion is projectingly provided on the swinging support portion so as to be opposed to an outer peripheral surface of a lower portion of the roller.
With the arrangement of the first feature, the base ends of the pair of support wall portions are connected to each other by the lower connecting wall. Therefore, the rigidity of supporting the support shaft by the support wall portions is increased, and the rigidity of the entire rocker arm is also increased. The lower connecting wall is disposed while effectively utilizing space between the roller and the swinging support portions, and the size of the rocker arm is not increased due to the lower connecting wall.
According to a second aspect and feature of the present invention, in addition to the first feature, the lower connecting wall is located in proximity to and opposed to the outer peripheral surface of the lower portion of the roller to such an extent that oil can be once retained between the lower connecting walls and the rollers. With such arrangement, the oil can be once retained between the lower connecting wall and the roller, and the oil retained between the lower connecting wall and the roller can be guided to the bearing between the roller and the support shaft to reduce the resistance to the rotation of the roller.
According to a third aspect and feature of the present invention, in addition to the first feature, the rocker arm is formed from metal by injection molding. With the above feature, it is possible to simply form each of the rocker arms having a relatively complicated structure in which the lower connecting wall protrudes from the swinging support portion. Thus, it is possible to easily form the rocker arm to be of an optimal shape while taking an increase in rigidity and a reduction in weight into consideration.
According to a fourth aspect and feature of the present invention, in addition to the second feature, the valve operating system further includes an urging means for biasing the rocker arm in a direction to bring the roller into rolling contact with the valve operating cam, the urging means being put in abutment against a receiving portion which is projectingly provided at a lower portion of one of the support wall portions and connected to one end of the lower connecting wall in an axial direction of the support shaft. With such arrangement, the rigidity of the receiving portion receiving a load from the urging means can be increased by the lower connecting wall.
According to a fifth aspect and feature of the present invention, in addition to the third feature, the valve operating system further includes an urging means for biasing the rocker arm in a direction to bring the roller into rolling contact with the valve operating cam, the urging means being put in abutment against a receiving portion which is projectingly provided at a lower portion of one of the support wall portion and connected to one end of the lower connecting wall in an axial direction of the support shaft. With such arrangement, not only the rigidity of the receiving portion receiving a load from the urging means can be increased by the lower connecting wall, but also the rocker arm having the receiving portion integrally provided thereon can be formed easily.
According to a sixth aspect and feature of the present invention, in addition to the first feature, the support shaft is supported between the support wall portions with opposite ends of the support shaft being fitted in the support wall portions, at least one of the support wall portions having a receiving portion integrally provided thereon in a range corresponding to at least a portion of that area of the support shaft which is fitted into the one support wall portion, the receiving portion being disposed at a location radially outside the support shaft, and wherein an urging means is provided for exhibiting a spring force for urging the rocker arm in a direction to bring the roller, which is rotatably supported on the support shaft with the bearing interposed therebetween, into rolling contact with the valve operating cam, the urging means being put in abutment against the receiving portion.
With the arrangement of the sixth feature, it is possible to simplify the structure of the rocker arm in such a manner that the receiving portion is provided radially outside the roller. At the same time, the receiving portion does not protrude from the rocker arm in the axial direction of the support shaft. Therefore, it is possible to avoid an increase in size of the rocker arm in the axial direction of the support shaft, and the inertial weight is decreased. Therefore, it is possible to conveniently accommodate the high-speed rotation of the internal combustion engine. In addition, the rigidity of supporting the support shaft on the one support wall portion can be increased by the provision of the receiving portion.
According to a seventh aspect and feature of the present invention, in addition to the sixth feature, an oil passage is provided in the one support wall portion to extend along a plane which extends perpendicular to the axis of the support shaft and through an abutment point between the receiving portion and the urging means. With such arrangement, it is possible to compensate for a decrease in weight of the one support wall portion due to the provision of the oil passage which is a cavity, by the receiving portion, thereby improving the balance in weight between the support wall portions. Moreover, it is possible to avoid a reduction in rigidity of the one support wall portion due to the provision of the oil passage by providing the receiving portion.
According to an eighth aspect and feature of the present invention, in addition to the sixth feature, the rocker arm is formed from metal by injection molding. With such arrangement, a fitting bore for fitting the support shaft therein can be defined in the rocker arm simultaneously with the formation of the rocker arm, and the number of post-processings can be decreased to contribute to an enhancement in productivity.
According to a ninth aspect and feature of the present invention, in addition to the seventh feature, the rocker arm is formed from metal by injection molding. With such arrangement, even if the cross sectional shape of the oil passage is out of round, it is possible to define the oil passage simultaneously with the formation of the rocker arm, thereby providing an enhancement in productivity and increasing the degree of freedom in designing the cross sectional shape of the oil passage.
According to a tenth aspect and feature of the present invention, in addition to the first feature, a notch recessed on a side opposite to a spark plug insertion tube mounted in the cylinder head is provided in that portion of the swinging support portion of the rocker arm, which is opposed to the spark plug insertion tube, and at least a portion of the lower connecting wall and at least a portion of the notch are disposed in the same plane perpendicular to a swinging axis of the rocker arm. With such arrangement, the spark plug insertion tube and the rocker arm can be disposed in close proximity to each other to contribute to a reduction in weight of the rocker arm and a reduction in size of a valve operating chamber defined in the internal combustion engine in such a manner to accommodate the valve operating system in the engine. Moreover, it is possible to compensate for the reduction in rigidity of the swinging support portion due to the provision of the notch by the lower connecting wall.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.